1. Field of the Invention
The present invention relates to servo control systems and more particularly to electronic governors controlling the rate of rotary power plants.
2. Description of the Prior Art
Control devices for regulating the speed of various power plants have been known in the past. In particular, regulation of internal combustion engines used with small electric power generators is often critical both in frequency and in the total power output. For this reason power plants designed for such unattended use have been provided with various speed regulators, typically in the form of regulating servos. A servo-loop adapted for such regulation most often centers around a tachometer pick-off, where the output of the tachometer is normally converted to a D.C. voltage compared at a summing amplified with a reference voltage to produce an error signal correcting the engine speed. A typical tachometer however is generally configured as an A.C. device. Thus, the output of the tachometer is normally cyclic and is converted from such cyclic form to a D.C. signal for comparison.
Alternatively, servo systems generally referred to as A.C. servos, avoid this rectification of the tachometer output by providing a servo loop which operates on the basis of A.C. signals. Systems of this kind however, all include either phase detection or complex amplification and therefore are not much simpler in their structure from the most basic D.C. servos.